At present many countries are interested in the manufacture of such current-conducting compositions, since the latter combine the advantages of such different components as polymers and metals.
They feature high corrosion resistance, processibility into shaped articles and the ability of being used under multiple deformations; they can replace critical non-ferrous and precious metals.
The known current-conducting compositions contain a polymeric base and a filler. As the polymeric base elastomers (often silicone ones) are used, as well as thermoplastics (polyethylene, polypropylene, copolymers of both), phenol-formaldehyde and epoxy resins. As the current-conducting fillers carbon blacks are employed such as acetylene carbon black, gas carbon black, lamp carbon black, channel carbon black. To improve the current conductivity, elasticity and durability of current-conducting compositions, the carbon black surface is treated with various reagents.
The company Canric Petriks Chemicals has developed a whole range of organotitanates for treating fillers with a view to improving the electrical conductivity and other properties of current-conducting compositions (cf. Plast. Technol., 1975, 22, No. 8, p. 71).
In a number of publications it has been suggested to introduce calcium, barium, strontium in a combined or elemental state during the combustion of a hydrocarbon stock in order to improve electrical conductivity of a filler - carbon black (cf. British Pats. Nos. 2,098,972 and 2,094,773).
In recent years a carbon black of the brand "Ketjenblack E.C." available from the company "Akzo-Chemie, Niederlande" has acquired an extensive use as a filter. It comprises a gas carbon black obtained as a result of combustion of a hydrocarbon feedstock with special additives ensuring its high porosity and an enormous surface area due to the presence of a great number of hollow particles. The carbon black "Ketjenblack E.C." has the electrical resistance (at the density of 180 kg/m.sup.3) of 0.005 Ohm.multidot.m, its yield is 5%, cost: $2,500 per ton; it is produced on a limited scale and is but hardly available. An electrically-conducting composition containing 15 parts by mass of this carbon black per 100 parts by mass of a polymer has an electric resistance of not more than 0.1 Ohm.multidot.m (cf. U.S. Pat. No. 3,723,355).
Known in the art is a process for producing a carbon-plastic electrode structure for an electrochemical device (U.S. Pat. No. 4,164,068), wherein a thin current-conducting carbon-plastic sheet is injection-moulded from thermoplastics or thermosetting resins filled with carbon blacks of brands "Ketjenblack E.C." (Noury Chemical Corp., New York) and "Vulkan XC-72" (Cabot Corp.) A carbon-plastic sheet has an electric resistance within the range of from 0.001 to 0.05 Ohm.multidot.m.
Known is a current-conducting composition (cf. U.S. Pat. No. 4,273,097) containing 7 parts by mass of a carbon black in the form of hemispherical particles with the surface area of 900 m.sup.2 /g (which corresponds to characteristics of the carbon black "Ketjenblack E.C.") having an electrical resistance with-in the range of from 0.01 to 1.00 Ohm.multidot.m.
A process is known for the production of polymeric compositions with an electric resistance below 10.0 Ohm.multidot.m by way of filling polyurethanes, epoxy and phenolformaldehyde resins with 0.15 to 2% by mass of current-conducting carbon fibres (cf. British Pat. No.1,570,249).
Known in the art is a process (cf. Japanese Pat. No. 55-26503) comprising manufacture of a flexible sheet material with a thickness of 0.15-0.20 mm having resistivity within the range of from 0.001 to 1.0 Ohm.multidot.m which is achieved by filling polyethylene, polypropylene and polyurethane with graphite and gas carbon black.
Known is a current-conducting composition (FRG Pat. No. 2,845,671) based on a thermoplastic filled by modifying additives and a carbon black with a specific surface area of 70 to 90 m.sup.2 /g intended for the formation of a semiconducting layer of a cable insulation and having resistivity of 4.5 to 5.0 Ohm.multidot.m.
U.S. Pat. No. 3,723,355 teaches a current conducting polymeric composition and a process for producing same. It has improved extrusion characteristics and abrasion resistance; it consists of 100 parts by mass of an elastomer, 40 to 400 parts by mass of a non-conducting filler and 2-15 parts by mass of gas-treated carbon with a surface area of 300-1,500 m.sup.2 /g, micropore void volume of up to 3 ml/g, macropore volume of 2-4 ml/g, as well as of a plastifying agent taken in the ratio of 1:1 to the gastreated carbon. Optimal results, as regards the resistivity, (.delta.=0.4 Ohm.multidot.m) are obtained by filling 100 parts by mass of an elastomer with 15 parts by mass of gas-treated carbon and 100 parts by mass of alumina (in the absence of triethanolamine).
As it is seen from the above-described prior art, good current-conductance characteristics of polymeric compositions depend mainly on current-conducting fillers, i.e. special carbon blacks having high structurization and a well-developed surface; on mixtures of carbon blacks with graphites, as well as with powders of noble metals. These carbon blacks necessitate high capital expenditures for their manufacture, wherefore they are expensive and rarely available. They have but a low processibility, wherefore their distribution within a polymeric matrix is hindered, thus causing difficulties in the production of polymeric compositions and impairing the stability of the resistivity of such compositions. The attained level of current-conductivity of polymeric compositions containing such carbon blacks, though covering the range of 0.00001-10.sup.8 Ohm.multidot.m, but is actually unknown due to the absence of data on the degree of compression of samples therefrom and the measurement procedures.
It is an object of the present invention to provide current-conducting composition having low resistivity, stable in time and during its processing.